Originally Posted by
Annandaler
Correct - the 5A driver sells nothing; and you can't buy any passes at the airport. Note that while the One Day Pass for $9 could be useful it has restrictions: it is a rail-only pass, and it can't be used before 9:30am on weekdays.
If the OP has enough time before the trip to the DC area, you can buy a SmarTrip card in advance. It costs $30 - $5 for the card, and it includes $25 worth of fare. There are no mailing or handling fees added. The SmarTrip card can then be used for the 5A bus trip into town, and all the other Metro rail and bus travel. See:
http://www.wmata.com/fares/purchase/store/
But a one day pass may still provide better vale. I suggest thebOP total their fares for the metro trips and compare it to the flat fare of a one day pass. Note the time of daynfor travel can effect the fare price